This is a simple tomato sauce by Samin Nosrat via NY Times.
Equipment Medium Dutch oven Large bowl Hand/immersion blender, blender, food processor, or food mill Ingredients 6 tablespoons extra-virgin olive oil 5 cups diced yellow onions, red onions or shallots Fine sea salt 1 (28-ounce) can whole peeled, diced, crushed or puréed tomatoes 4 garlic cloves, thinly sliced 2 tablespoons tomato paste 4 to 5 basil stems ¼ teaspoon red-pepper flakes Preparation Cook Onions Set a medium Dutch oven or similar pot over medium heat, and add 4 tablespoons olive oil. When the oil shimmers, add onions and a pinch of salt. Reduce heat to medium-low and cook, stirring regularly, until onions are lightly golden and tender, 16 to 18 minutes. While the Onions Cook In the meantime, pour the tomatoes into a large bowl and use hands to crush, if using whole tomatoes. Pour about 1 1/2 cups water into the can and swirl to rinse any remaining purée off the sides. Add the water to the tomatoes in the bowl and set aside. Add Garlic & Tomatoes Once onions are soft and golden, add garlic and cook, stirring until it threatens to turn golden, about 90 seconds. Add tomato paste and cook until color deepens, about 3 minutes. Add tomatoes and season with salt. Add basil stems and red-pepper flakes. Simmer Stirring regularly, allow sauce to come to a boil, then reduce heat to low, cover and simmer until sauce tastes savory and all raw tomato flavor is gone, about 45 minutes. Finish Taste and adjust seasoning with salt and add remaining 2 tablespoons oil. Use a hand blender to purée, pass through a food mill or let cool, then purée using a blender or food processor. Tomato sauce can be made 1 day in advance and refrigerated or frozen up to 3 months.